With the continuously expanding of the scale of computer networks and the rapidly developing of large internets, routing technology has become gradually a critical technology among the network technologies, and routers have become the most important equipments in a network. A router operates at the third layer of the OSI (Open System Interconnect) Model, which is named the network layer. A router differentiates different networks to implement interconnection and isolation between networks and keep the independence of the individual networks by utilizing the ‘logic’ network address (i.e., IP address) defined in the network layer.
During the transition of the current telecommunication network from circuit-based technology to packet-based technology and the evolution of multiple independent dedicated service networks toward an integrated multi-service network, IP (Internet Protocol) technology has been widely accepted as the public user network interface of the Next Generation Network service. With the introducing of the MPLS (Multi-protocol Label Switching), an IP network is not only able to keep sufficient flexibility but also able to provide manageable and operable services that may be better than best-effort delivery service, while possessing certain connection oriented characteristic. It is an important feature of the Next Generation Network to provide abundant public operating services by the coexistence and cooperation of the intelligence inside a network and the intelligence at the edge of the network. Accordingly, a multi-service edge router at the edge of a network is very important and necessary for constructing an integrated multi-service network.
TCP/IP (Transmission Control Protocol/Internet Protocol) technology, as originally conceived, offers only a best-effort delivery service without QoS (Quality of Service) guarantee. However, it is difficult for the best-effort delivery service to meet the requirements of multimedia service for delay, jittering and packet loss rate in a multi-service environment, since different services and users have different requirements for quality and security of network service. In view of this, the QoS technologies and mechanisms, such as InterServ (Integrated Service), DiffServ (Differentiated Service) and policy control, have been presented. Nevertheless, the problem of QoS in a packet-based network has not been resolved up to now. The relative QoS mechanism provided by DiffServ can not find a solution to the traffic congestion or optimize the performance of a network, and the quality of network service provided by DiffServ is uncontrollable, immeasurable and not absolutely guaranteed. The absolute QoS mechanism provided by InterServ requires large network overhead, and has a serious problem on extensibility regarding the number of application flows supported and network scale. MPLS traffic engineering technology still can not provide a real-time control system for scheduling of application flow level. Considering the construction of the next generation network by employing IP techniques, the QoS problem has become a critical bottleneck to be broken during network convergence and evolution.
Today's IP networks are all of layered architecture, i.e. all contain a packet-based core network and various types of access networks in order to achieve good manageability, stability and extensibility. The core network routes and switches packets in high speed, having high reliability and redundancy. The access networks support various user access modes, such as Ethernet LAN, xDSL (Digital Subscriber Line), HFC (Hybrid Fiber Coaxial Cable), etc., and provide network service control functions such as access control, authentication billing, network security, VPN (Virtual Private Network) and QoS classification, and the like.
An edge router locates at the egress of an access network and the ingress of a core network, the multi-service supporting capability of which is the most important with respect to whether the network can support various services, and the QoS-supporting capability of which plays an important role in QoS framework of an IP network. A multi-service edge router has to possess capabilities of flow classification, traffic control (including metering, marking, dropping/shaping and queuing) and traffic aggregation.
In the IntServ model, a service traffic flow sender installs and refreshes in advance the information of the resource reservation state at the respective forwarding nodes on the service traffic flow path(s) via Resource Reservation Protocol, thus establishing a virtual connection with QoS guarantee. The respective forwarding nodes recognized and schedules each of the service traffic flows according to the resource reservation soft state (means that a periodic maintaining of the resource reservation refresh packets is needed). To maintain the virtual connection, the service traffic flow sender periodically refreshes the resource reservation soft state to the network via Resource Reservation Protocol until the application layer shows a request to end the reservation or the network feedback can not provide reservation for the application. Resource Reservation Protocol is a path-coupled signaling protocol, and the path of the protocol packet is completely the same as the service traffic flow path.
The functional block diagram of the respective forwarding nodes (including the edge router) in the IntServ model is shown in FIG. 1, the functions include RSVP (Resource Reservation Protocol) protocol processing, RSVP soft state maintaining, routing, policy control, admission control, packet classification, packet forwarding and packet scheduling. To support the IntServ model, the edge router has to possess these functions as well, all of which are directed to application flows including admission control, policy control, RSVP state maintaining, packet classification, queue scheduling. There will be thousands of or even more states, classifications and queues to be maintained if the granularity of control is refined to application flow level.
Although the Intserv model can be used to achieve a refined granularity of resource control in application flow level, it is necessary for the routing equipments (including the edge router) to record a large amount of RSVP soft state information of application flows and to handle a great deal of periodic RSVP soft state refresh packets. Each of the application flows occupies a scheduling queue, thus resulting in a high requirement for the performance of the routing equipments, and a serious issue of extensibility in application to medium/large networks. For this reason, such QoS technology is not used widely in the IP network operated by the telecommunication operator.
Even if IntServ is only applied in access networks and DiffServ or MPLS TE (Multi-protocol Label Switching Edge Router) is used in a core network, the burden of the edge router is not relieved at all. The edge router still has to record a large amount of RSVP soft state information and to handle a great deal of periodic RSVP soft state refresh packets, and to provide the aggregating and mapping functions of QoS classification.
The process of the classification and the conditioning of traffic by an edge router in DiffServ model is shown in FIG. 2: the ingress node at edge of a network performs classification and conditioning, including metering, marking, dropping and shaping, to the packet traffic according to the static SLA (Service Level Agreement). Wherein the marking refers to the process of setting a value for the DSCP (Differentiated Service Code Point) domain in each packet. Each DSCP code represents a class of aggregated traffic (at most 64 classes), and it is required that the same specific QoS forwarding process is performed at all the network nodes. Each hop node inside the network forwards a packet depending on the value of the DSCP domain according to the configured QoS mechanism, such PHB (Per-Hop Behavior) includes resource allocation, queue scheduling, dropping policy, etc.
The DiffServ model employs the concepts of coarse classification and aggregation in which different classes receiving different services in the network, without negotiating in advance on resource reservation. The control is coarser grained, there are generally 6 QoS classes (64 classes at most), each of the classes having several queues. By conditioning the behavior of the boundary node(s), the incoming traffic to each QoS class of the network may be controlled. The states of the flows are not recorded inside the network, but are processed for each packet according to the marked QoS type, thereby the signaling protocol processing is omitted.
FIG. 3 is a functional block diagram of an edge router in the DiffServ model.
The input interface and the output interface both perform classification, metering, processing and queue scheduling, all of which are performed with respect to the level of traffic aggregation, without signaling negotiation and state maintaining of application flow, thereby the number of the queues required are reduced greatly. The specs of flow classification and PHB behavior for each class of service can be configured locally by command lines, or be configured by network management server through provision of SNMP (Simple Network Management Protocol) Interface, or be configured by policy server through provision of COPS (Common Open Policy Service) Interface.
Such DiffServ model of providing classified services is more suitable for a large-scale core network. However, its flow classification spec is rather coarse grained, and is generally based on physical port or logic port instead of application flow. Due to the temporality and frequent variations of the application flow, the identity (the initiation and destination IP addresses, port numbers and protocol types) of the application flow and the desired QoS type are not known by the network management and the policy management, thus an edge router is unable to have the ability of classification and identification in application flow level by configuring the management interfaces. Moreover, because the service of the same class will share the resource of this class, and there will exist a certain degree of resource competition between those services with the same priority, the end-to-end QoS may not be guaranteed.
The operators generally try to avoid the problem of resource competition between services with the same priority according to the statistic characteristic by means of a large bandwidth and a light load, that is to say, the average utilization of the control resources of a core network is no more than 50% or 70%, and the average utilization of resource for the services with higher priorities is no more than 20%. However, the cost of a network with a large bandwidth and a light load is much high, the wider the bandwidth is, the bigger the absolute value of the waste is. Once the load is over 50%, serious traffic congestion problem will occur; furthermore, what the DiffServ provides is only a relative QoS, namely a better QoS than that of the best-effort delivery, which can not provide end-to-end absolute QoS guarantee for the application flow.